The Supercharger HP features the contoured main body of the 4150 HP and gets tumble polished for a fine shine. Uniquely, its power valves reference the intake manifold vacuum below the supercharger, allowing power valves to operate as they should (based off intake manifold vacuum). A power valve adds enrichment to the main metering system under load (low vacuum) conditions. Without this external referencing, power valves would just read boost pressure, which has no bearing on engine load.